The present invention relates to labels from which printed ink can be removed, and it also relates to bottles fitted with these labels, processes for their ink removal, processes for their recycling, and their recycled polymer pellets.
In recent years, the use of polymer bottles, particularly those made of thermoplastic polymers, has been increasing year after year because of their excellent resistance to breakage, lightweight properties, and transparency as compared with conventional bottles made of glass, metals, or other materials. In particular, the conversion from conventional bottles to polymer bottles has remarkably progressed in the beverage industry, and they are used in great quantity, extending from small bottles to large bottles. Among other bottles, the use of bottles made mainly of polyethylene terephthalate (hereinafter referred to as xe2x80x9cPET bottlesxe2x80x9d) has remarkably risen.
Great interest has recently grown in global environmental problems, and there are great demands for some measure against the problem how to recycle bottles made of thermoplastic polymers. Much attention has been paid to the recycling of bottles made of thermoplastic polymers, particularly PET bottles, and early development is required for their recycling system. In general, PET bottles are fitted with various labels, e.g., stretch labels made of polyolefins; heat-shrinkable labels made of polyesters, polystyrene, polyvinyl chloride, or other polymers; and tack labels made of polypropylene or other polymers. In recycling PET bottles, they are usually collected from general consumers without removal of their labels, and then brought to the recycling interests. These bottles are washed, and their labels are removed by primary crushing, at which time, however, the crushed polymer materials may still include the labels in great quantity. Therefore, the conversion of PET bottles into recycled polymer pellets requires subsequent many steps such as secondary crushing, specific gravity separation of labels in a liquid, dehydration and drying, specific gravity separation of labels by air blowing, and pelletization. FIG. 3 is a flow chart showing a typical process for recycling thermoplastic polymers as their pellets from conventional labeled bottles.
In the recycling process for conventional labels and bottles fitted with these labels as described above, the labels are separated in various steps of separation; however, the recycling ratio of starting materials is decreased with an increase of purity in the recycled thermoplastic polymers. Further, the recycled thermoplastic polymers are contaminated with label resins, ink, and other impurities. In particular, the incorporation of ink may cause a serious problem that the recycled polymer pellets are colored as a whole even when contaminated in small quantity.
In order to achieve the effective recycling of bottles, the incorporation of labels and label ink should be prevented to increase the purity of recycled thermoplastic polymers. Many improvements have been made so far in the thermoplastic polymers as the label materials, and there have been proposed labels made of polymers (e.g., polystyrene, polyolefins such as polyethylene and polypropylene) that can easily be separated by specific gravity and may have low specific gravity than polyethylene terephthalate. The formation of ink layers cancels the advantage of low specific gravity, making it impossible to carry out complete separation.
There have also been proposed labels made of the same polyesters as used in PET bottles, which cause no problem even when incorporated into the PET bottles; however, no separation of ink layers can be made from the labels and the problem of how to prevent the coloring of recycled polymer pellets has not yet been solved.
In addition to the problem of coloring, there has not yet been solved another problem that the resulting recycled polymer pellets have insufficient purity. In particular, various oligomers including cyclic trimeric oligomers formed in the recycled polymer pellets cause a serious trouble that the molds or nozzles used in the spinning, extrusion, injection, or any other molding of the recycled polymer pellets may often be fouled with these oligomers and the products may often be stained with these oligomers to lower their quality. Therefore, the recycled polymer pellets obtained in this manner are difficult to use and they can find only limited applications.
Under these circumstances, the present inventors have intensively studied to solve the above-described problems and troubles in the recycling process for conventional labels and bottles fitted with these labels, thereby completing the present invention. In other words, it is an objective of the present invention to provide labels with easily removable ink layers, bottles fitted with these labels, processes for removing ink layers from these labels, processes for removing ink layers from these labels on the bottles, processes for recycling the ink-removed labels and bottles, as well as recycled polymer pellets.
Thus, a label of the present invention has a thermoplastic polymer film and an ink layer formed on at least one surface thereof, and the ink layer is removable in alkaline hot water.
Another label of the present invention has a thermoplastic polymer film and an ink layer, between which an intermediate layer removable in alkaline hot water is formed.
The bottle of the present invention has the label as described above. When the thermoplastic polymer film of the label is a heat-shrinkable film, the label may have a heat shrinkability of 0.1% or higher but lower than 80% along the circumferential direction of the bottle.
The process for ink removal from the labels or bottles as described above according to the present invention involves immersing the labels or bottles in alkaline hot water to remove the ink layers from the labels. The removed ink may be dried, pulverized, and separated from the labels by air blowing.
The process for recycling the bottles as described above according to the present invention involves melting the bottles fitted with the labels from which the ink layer has been removed by the above process for ink removal and forming the melt into recycled polymer pellets.
The recycled polymer pellets of the present invention are obtained by the above recycling process.